Method of broaching a blank upon a shaft

ABSTRACT

A STEEL SHAFT HAVING PERIPHERAL LANDS IS BROACHED BY A SPLINED CARBIDE BLANK TO FORM A BROACHED ASSEMBLY HAVING INTERFACES BETWEEN THE LATERAL FLANKS OF THE LANDS AND LATERAL FLANKS OF THE SPLINES. THE INNER AND OUTER PERIPHERAL PORTIONS OF THE STEEL SHAFT ARE SPACED FROM THE CARBIDE BLANK TO PREVENT RADIAL STRESSES FROM BEING PRODUCED DURING BROACHING AND TO ACCOMMODATE THERMAL EXPANSIONS IN THE BROACHED ASSEMBLY. CIRCUMFERENTIAL SHIP GROOVES ARE PROVIDED IN THAT PORTION OF THE SHAFT WHICH IS TO BE BROACHED BY THE CARBIDE BLANK TO PREVENT CONTINUOUS CHIPS FROM FORMING DURING THE BROACHING PROCESS WHICH COULD SEIZE ON THE CUTTING FACE OF THE CARBIDE BLACK. THE CARBIDE BLANK OF THE BROACHED ASSEMBLY RESINS DISPLACEMENTS RELATIVE TO THE STEEL SHAFT. THE INTERFACES MAY BE ANGULARLY DISPOSED TO ALLEVIATE LARGE CIRCUMFERENTIAL THERMAL STRESSES.

1971 s. J. SOBANSKI ETAL 3,619,882

METHOD OF BROACHING A BLANK UPON A SHAFT l Filed 001;. 27, 1969 3 2 FIG- 2 3/ J2 zi /J /fl m ZZ FIG 4 z/vvsA/Tares STANLEY I SOB/WSK] OT/L F/MST/PZFOPTE GODWJ/V L. NOE/.1.

BY EWQJMJ ATTOPNEY United States Patent O "ice 3,619,882 METHOD OF BROACHING A BLANK UPON A SHAFT Stanley J. Sobanski and Otil F. Mastriforte, Newington, and Godwin L. Noel], New Hartford, Conn., assignors to Chandler Evans Inc., West Hartford, Conn.

Filed Oct. 27, 1969, Ser. No. 869,641 Int. Cl. B21d 53/28; B21h /00; B2lk 1/30 US. Cl. 29159.2 4 Claims ABSTRACT OF THE DISCLOSURE A steel shaft having peripheral lands is broached by a splined carbide blank to form a broached assembly having interfaces between the lateral flanks of the lands and lateral flanks of the splines. The inner and outer peripheral portions of the steel shaft are spaced from the carbide blank to prevent radial stresses from being produced during broaching and to accommodate thermal expansions in the broached assembly. Circumferential chip grooves are provided in that portion of the shaft which is to be broached by the carbide blank to prevent continuous chips from forming during the broaching process which could seize on the cutting face of the carbide blank. The carbide blank of the broached assembly resists displacements relative to the steel shaft. The interfaces may be a'ngularly disposed to alleviate large circumferential thermal stresses.

BACKGROUND OF THE INVENTION The invention relates generally to metal working and particularly to a method of broaching together two dissimilar materials. The invention further relates to assemblies of two dissimilar metals which incorporate features to overcome the stresses induced by thermal expansions. The invention also relates to gear and journal assemblies in gear pumps.

When the inlet port of a gear pump containing an intermeshing pair of gears is connected to a source of fluid, rotation of gears in one direction will cause the liquid to be drawn through the inlet port into the housing and carried around in pockets formed between the adjacent teeth of both gears and the housing and thence discharged to the outlet port. The liquid is drawn into the housing due to the increasing free space between the housing adjacent the inlet port as the teeth of the two gears move out of engagement, and is discharged due to the decreasing free space within the housing adjacent the outlet port as the teeth move into engagement, inlet and outlet ports being substantially isolated from one another by small clearances between the teeth and the housing.

The volumetric eificiency of such a gear pump depends upon the closeness of the fit between the tips of the gear teeth and the enclosing housing. When such a gear pump is utilized to pump a fluid containing a highly abrasive contaminant, the clearances between the tips of the gear teeth and the surrounding housing rapidly become enlarged and the pump volumetric efliciency falls off. One well known method of providing a solution to this problem of rapid high wear is to insert a wear block in the pump housing adjacent the pump outlet. This Wear block is urged by discharge pressure into engagement with the periphery of the gear teeth adjacent the pump discharge area.

It has been customary to manufacture the wear block and the gears of an extremely hard wear resistant material, such as tungsten carbide, so that the peripheral engagement of the gear teeth and the mating arcuate wiping surfaces of the wear block present a surface that can withstand the highly abrasive action of the contaminant fluid. However, the use of tungsten carbide gears creates cer- 3,619,882 Patented Nov. 16, 1971 tain problems, prominent among which, is the manner of attachment of the gear to the shaft or journal. A one-p ece carbide gear and shaft assembly would not be practical due to the bending stresses imposed upon the shaft by the pressure load on the gear and the necessary splines required in the shaft for attachment to a drive means. As carbide is relatively brittle, the shaft and/or splines are likely to fail when subjected to repeated loading. Another reasons for not utilizing such an assembly is that prohibitive bearing wear may result from the use of a carbide shaft.

It would, of course, be possible to braze the carbide gear upon a steel shaft but it has been found that this method of attachment is unsatisfactory. All metals when heated, expand, and, on cooling, return to their original size. Since tungsten carbide has a coefficient of thermal expansion approximately half that of steel in a range from room temperature to about 1250 F, the expansion of carbide during the brazing operation is only about half that of the steel shaft and it is this phenomenon which creates most of the problems in brazing. When cooling from the brazing temperature the steel shaft tends to contract more than the carbide and in doing so creates high stresses in the carbide. The brazed joint between the carbide gear and steel shaft has also been found to be prone to fatigue failure when subjected to repeated torsional stresses.

A method was investigated to solve the above problem of attaching a carbide gear to a steel shaft, which involved broaching a carbide gear having internal spline serrations upon a steel shaft to shear mating spline serrations thereon for locking the two component parts together. It was found that this method caused internal radial stresses to develop in the carbide which were manifested by failure of the carbide blank as gear teeth were cut thereon.

SUMMARY OF THE INVENTION The instant invention provides a method by which a blank, made of a hard material, may be broached upon a shaft, made of softer material, to securely attach the blank to the shaft while eliminating radial stresses in the blank. A blank, made of a hard material, having a hollow portion which includes a recess bounded by lateral flanks is broached upon a shaft having a peripheral land which is slightly wider than the recess. During the broashing process the lateral flanks of the recess broach the lateral flanks of the land. The inner and outer circumferential peripheries of the shaft are spaced from the blank to accommodate a limited differential expansion of the blank and shaft and prevent radial stresses from developing in the blank during broaching. The broaching of the blank on the shaft results in a mechanical lock being established between the two components which enables the blank to resist axial displacements relative to the shaft. The invention thus provides a method of rigidly securing a carbide blank to a steel shaft without producing internal radial stresses in the carbide blank while allowing for a limited differential expansion of the two components.

It is accodingly a primary object of the invention to provide a method for rigidly attaching a blank to a shaft.

Another object of the invention is to provide a method of attaching a carbide blank to a steel shaft which does not induce radial stresses in the carbide blank.

Yet another object of the invention is to provide a method of fixedly attaching a blank to a shaft which allows for a limited differential thermal expansion of the two components.

A further object of the invention is to provide a method for attaching a carbide gear to a steel shaft to form an assembly which is suitable for inclusion in a gear pump.

The foregoing and other objects and advantages will become apparent in view of the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of a carbide gear and steel shaft assembly broached in accordance with the invention.

FIG. 2 is a fragmentary longitudinal view of the steel shaft per se.

FIG. 3 is a transverse sectional view of the assembly of FIG. 1 taken along the line 33.

FIG. 4 is a transverse view of another steel shaft and carbide blank assembly broached in accordance with the invention which incorporates a feature to accommodate large differential thermal expansions.

DETAILED DESCRIPTION Turning now to FIGS. 1 and 2 wherein there is shown a broached assembly, a hollow carbide blank structure 8 is secured to a steel shaft 10. The blank 8 has teeth 12 cut thereon so as to form a shaft and gear assembly adapted to be incorporated in a gear pump. Shaft has a plurality of longitudinally extending lands 14 on the periphery thereof. Each land 14 includes an outer peripheral surface 16 and lateral flanks 18 and 20. The inner peripheral surface of shaft 10 is defined by surfaces 22 which extend between the opposite flanks of neighboring lands.

Blank 8 comprises a plurality of longitudinally extending splines 25 having lateral flanks 26 and 28. The interior peripheral surfaces 30 of splines 25 extend between flanks 26 and 28. Longitudinally extending recesses 24 are formed between neighboring splines 25, the recesses partially receiving the lands of shaft 10 after the broaching process has been accomplished. As shown in FIG. 2 after broaching of the blank 8 upon the shaft 10 the outer peripheral surfaces of lands 14 and the inner peripheral surfaces 22 of shaft 10 are spaced from the carbide blank 8. This geometrical relationship not only prevents radial stresses from being produced in the blank during the broaching process but also allows for a limited differential thermal expansion of the carbide blank and steel shaft.

Turning now to FIG. 3 wherein the detailed land arrangement is shown it will be observed that steel shaft 10 comprises an enlarged portion generally designated at 32. Enlarged portion 32 is tapered at both ends to form an angle of 150 with the surface of the shaft to facilitate the machining thereof and the broaching of the blank thereon. Lands 14 each comprise a plurality of circumferentially extending chip grooves 34 which are machined thereon to prevent the formation of long continuous chips during the broaching process.

Prior to broaching, splines 25 are cut into blank 8 by a conventional Eloxing process. The oppositely disposed flanks of neighboring splines are generally formed parallel to a radius which passes through the center of the recess between the splines, although the flank angle can be varied if desired when large temperature variations are anticipated, as is described more fully hereinafter. Lands 14 are then machined on steel shaft 10 such that flanks 18 and 20 are generally parallel to a radius passing through the center of the land. The transverse width of each of the lands 14 is initially slightly larger than is the transverse width of each of the recesses 24 to permit the respective lateral flanks of the recesses to breach the lateral flanks of the lands. This width differential should be of the order of a thousandth of an inch.

Blank 8 is secured in a suitable work holder and shaft 10 is placed in axial alignment with blank 8 such that the lateral flanks of each land respectively axially overlap the corresponding lateral flanks of each recess and the inner and outer peripheral surfaces of the shaft are radially spaced from the blank. Axial movement of the shaft relative to the blank then causes the flanks of the recesses to respectively cut into the lands. As the shaft is axially moved into the blank by a hydraulic press or other suitable drive member flanks 26 and 28 cut into the sides of land 14. As the shaft advances into the blank it will be noted that the only contact between the shaft and the blank is along the abutting flanks thereof by virtue of the spacing provided between surfaces 16 and 22 and the blank and therefore the radial stresses are not produced in the blank during the breaching process. After the broaching process has been completed and the blank substantially envelopes enlarged portion 32 of shaft 8, gear teeth are formed on the blank. Appropriate finishing operations are then performed upon the broached assembly to render the assembly suitable for incorporation in a gear pump. The steel shaft is preferably made of a soft steel such as Nitralloy, and if such is the case it may be desirable to finish the surface thereof by a nitriding process, this process being well known to those skilled in the art.

It will be noted that the broached assembly of FIGS. 1 and 2 is adapted to be used only in pumps which are not subjected to extreme variations in temperature (i.e., over 200 F.). When subjected to an increase in temperature surfaces 22 and 16 of the shaft 10 will be displaced closer to the blank 8 during this temperature change. During temperature increases lands 14 will, of course, produce circumferential stresses in the blank 8 by virtue of the larger coefficient of expansion of steel. However, these circumferential stresses should not induce failure of the blank 8 unless the temperature change is excessive.

If the application dictates that the shaft assembly should be able to accommodate significant temperature changes without becoming susceptible to failure because of the stresses induced in the blank, a shaft assembly as illustrated in FIG. 4 should be employed. The shaft assembly shown in FIG. 4 is the same as that of FIG. 1 with the exception of the angular relationship of the flanks of the lands and recesses to the shaft. Further, the assembly of FIG. 4 is broached by the same method described with reference to FIG. 1.

Referring to FIG. 4, a shaft assembly generally indicated at has a hollow carbide blank 42 broached upon a steel shaft 44. Blank 42 comprises a plurality of splines 46 which define recesses 47 and have flanks 48 and 50. The flanks of the splines form predetermined angles with the radial direction 2 and are cut to the desired flank angle by Eloxing. Shaft 44 has a plurality of lands 52 which have flanks 54 and 56 machined to the same angles as flanks 48 and 50. The outer and inner peripheral sur faces 58 and 60 of shaft 44 are spaced from the carbide blank as in the previously discussed embodiment. Lands 52 each have a circumferential width 2B that is measured along an arc midway of the radial depth of the lands. This are is a radial distance R from the center of shaft 44. When the assembly of FIG. 4 is exposed to a temperature change the difference in the expansion coeflicients of steel and carbide results in a differential expansion of the two components of the assembly.

The total resultant expansion E of points 62, which.

are defined by the intersections of the midway arcs along which the width 2B is measured and flanks 54 and 56 of lands 52, may be represented by a radial expansion E and a circumferential expansion E These expansions may be computed by the following equations wherein:

AT=Overall temperature change;

R=Radius of the point 62 on the interface between abut- Referring to FIG. 4 and assuming a uniform temperature change AT has been occasioned throughout the assembly, it is obvious that:

E =(A A )-AT-R (1) E =(A A )-AT-B 2 Bearing in mind that Equations 1 and 2 represent the components of the expansion of interface point 62, a resultant expansion E lying in the direction of the interface would require that:

But, in order for Equation 3 to be valid the tangent of the angle must be related to the component expansions as follows:

Tan 6=EC/ER Tan 0=B/R If this broaching is performed with both carbide and steel raised to the maximum temperature expected in operation and then allowed to cool, the assembly will automatically be capable of operating at that particular temperature without encountering unwanted interference.

It will thus be observed that as B, the midpoint width of a land increases, 0 correspondingly increases. If the selected values of B are small with respect to a given R significant stresses will be avoided along the entire interface between flanks 50 and 56. It will further be observed that as the assembly 1 undergoes a temperature change flanks 50 and 56 will slide along one another. Thus in this arrangement an increase in temperature results in sliding between the abutting flanks and movement of surfaces 58 and 60 towards blank 42.

It will be understood that the arrangement illustrated in FIG. 4 is not limited to any particular process of manufacture or materials but would find utility irrespective of the method of securing one component upon the other. Other modifications in the disclosed process and arrangements are contemplated within the scope of the invention.

We claim:

1. A method of attaching together a blank, made of a hard material, having a hollow portion which includes a recess bounded by lateral flanks, and a shaft, made of a material softer than that of the blank, having a peripheral land bounded by lateral flanks and an outer peripheral surface, which comprises:

aligning the shaft and the blank such that the flanks of the land respectively overlap the corresponding flanks of the recess and the inner and outer peripheral surfaces of the shaft are radially spaced from the blank; and

broaching the blank upon the shaft by causing relative axial movement between the blank and shaft such that the flanks of the blank respectively cut into the land adjacent the flanks thereof to securely mount the blank on the shaft.

2. A method, as defined in claim 1, wherein the blank is made of carbide and the shaft is made of steel.

3. A method of making a gear and shaft assembly which includes attaching together a blank, made of a hard material, having a hollow portion which includes a recess bounded by lateral flanks, and a shaft, made of a material softer than that of the blank, having a peripheral land bounded by lateral flanks and an outer peripheral surface, the attaching comprising:

aligning the shaft and the blank such that the flanks of the land respectively overlap the corresponding flanks of the recess and the inner and outer peripheral surfaces of the shaft are radially spaced from the blank;

breaching the blank upon the shaft by causing relative axial movement between the blank and the shaft such that the flanks of the blank respectively cut into the land adjacent the flanks thereof to securely mount the blank on the shaft; and

forming teeth on the blank to define a gear.

4. A method, as defined in claim 3, wherein the blank is made of carbide and the shaft is made of steel.

References Cited UNITED STATES PATENTS 1,157,666 10/1915 Bennett 29432 X 1,905,277 4/1933 Ewert 28753 SUX 2,038,554 4/1936 Edgar 28753 S 2,279,956 4/1942 Sipe 28753 S 2,317,070 4/ 1943 Le Tourneau 287--53 S 2,443,688 6/1948 McFarland 28753 S 2,519,035 8/1950 Esty 29-432 UX CHARLIE T. MOON, Primary Examiner US. Cl. X.R. 

